SimCity 2000

Freeland scenario:
Load and successfully complete the Las Vegas scenario within 10 years. A message will confirm that the secret level has been unlocked. It consists of flat terrain with no water, featuring a picture of Mario in the middle.
Information in this section was contributed by chkltwndrs.

Las Vegas scenario:
Successfully complete the six default scenarios. Then, grow a city that has a population of over 100,000 and save the game.
Information in this section was contributed by chkltwndrs.

Hint: Control tax money:
Lay low with your money and buy small amounts of everything. Keep low on residential, commercial, and industry. Build what the citizens want when you can afford it. Continue to do this until you start to progress in tax money.
Information in this section was contributed by John Marchick.

Hint: Easy money:
Enter the options and select "GRAPHS". Choose "Bond Payments", and go to issue all the money that you want to take out. Note: You are only issued a certain amount of money.
Information in this section was contributed by Troyspaceman.